Especially in the area of mobile handheld devices, for example mobile navigation devices, mobile personal digital assistants and mobile phones, especially so-called smartphones, there is a need and design trend to larger displays. The displays of these devices are usually provided with a touch-sensitive surface for detecting a user touching a surface of the display for operating the device. On the other hand, the overall size of the devices is required to be small enough to be held comfortable within one hand and to be stowed in a pocket or in a small handbag. Therefore, the bezels around the displays of mobile devices are getting smaller or they are completely omitted. Thus, the whole front surface of for example a mobile phone is covered by the display or touch screen. FIG. 1 shows such a mobile handheld device 10 having a touch screen 11 covering the whole front surface of the mobile handheld device 10. FIG. 1 furthermore demonstrates one of the challenges of such a design. The fingers of the hand holding the mobile phone 10 may touch the touch-sensitive surface 11 and this may be detected by a capacitive touch sensor and may cause usability problems. In the example shown in FIG. 1, the mobile handheld device 10 is held between fingers 40 to 42 on the left-hand side and the thumb and a part of the hand palm 43 on the right-hand side. However, due to holding the device 10, in the example shown in FIG. 1, the fingertips of fingers 41 and 42 are touching the touch screen 11 in areas 31 and 32, respectively, and a part of the hand palm 43 touches the touch screen 11 in area 33.
Therefore, there is a need to differentiate the fingers holding the mobile handheld device from the ones actually interacting with a user interface of the mobile device.